Chapter 18

Question 1

What are the two components of the mitochondria?

Answer 1

1) the inner membrane space between the outer and the inner membranes
2) the matrix, which bounded by the inner membrane

Question 2

Where does oxidative phosphorylation take place?

Answer 2

in the inner mitochondrial membrane

Question 3

T/F The inner membrane is permeable to nearly all ions and polar molecules.

Answer 3

False

Question 4

What is oxidative phosphorylation?

Answer 4

the electron-transfer potential of NADH or FADH2 is converted into the phosphoryl-transfer potential potential of ATP.

Question 5

T/F

A strong reducing agent (such as NADH) is poised to donate electrons and have a negative reduction potential.

Answer 5

True

Question 6

T/F

A strong oxidizing agent (such as O2) is ready to accept electrons and has a positive reduction potential.

Answer 6

True

Question 7

What is driving force of the electron transport chain?

Answer 7

the electron transfer potential of NADH and FADH2 relative to that of O2

Question 8

The released energy from the reduction of O2 with NADH generates a _________ that is used for the synthesis of ATP and the transport of metabolites across the mitochondrial membrane.

Answer 8

proton gradient

Question 9

__________ within the transmembrane complexes leads to the transport of protons across the inner mitochondrial membrane.

Answer 9

Electron flow

Question 10

__________ is special electron carrier that shuttles electrons from Complex I to Complex II.

Answer 10

Ubiquinone (Q)

Question 11

Where do the electrons of NADH enter the ETC?

Answer 11

Complex I

Question 12

How do electrons from NADH enter the ETC?

Answer 12

the initial step is the binding of NADH and the transfer of its electrons to FMN. Electrons are then transferred to series of Fe-S clusters and then passed on to Q

Question 13

T/F

When accepting two electrons, Q takes up two protons from the matrix as it is reduced to QH2.

Answer 13

True

Question 14

How do electrons from FADH2 enter the ETC?

Answer 14

electrons from FADH2 are transferred to Fe-S centers of Complex II and then to Q for entry into the ETC
(electrons can also be transferred through glycerol phosphate dehydrogenase)

Question 15

What is the function of Q-cytochrome c oxidoreductase (Complex III)?

Answer 15

to catalyze the transfer of electrons from QH2 to oxidized cytochrome c, a water-soluble protein, and concomitantly pump protons out of the mitochondrial matrix (2H+ to the cytoplasmic side)

Question 16

What is a cytochrome?

Answer 16

an electron-transferring protein that contains a heme group

Question 17

T/F
The iron ion of a cytochrome alternates between a reduced ferrous (+2) state and an oxidized ferric (+3) state during electron transport.

Answer 17

True

Question 18

How does Complex III accept electrons?

Answer 18

In addition to hemes, the enzyme contains an iron-sulfur protein with an 2Fe-2S center. This coordination stabilizes the center in its reduced form, raising its reduction potential so that it can readily accept electrons from QH2

Question 19

How does the Q cycle work?

Answer 19

Two QH2 molecules bind to the complex consecutively, each giving up two electrons and two H+. These protons are released to the cytoplasmic side of the membrane. One electron flows to a molecule of oxidized cyto c converting it to the reduced form. The second passes through the two heme groups of cyto b to an oxidized Q and reduces it to a semiquinone radical anion.

Question 20

T/F4
On the addition of the second electron, the Q radical takes up two H+ from the matrix side. The removal of these two protons from the matrix contributes to the formation of the proton gradient.

Answer 20

True

Question 21

How many protons are released to cytoplasmic side and how many protons are removed from the mitochondrial matrix in the Q cycle??

Answer 21

4

Question 22

What does cytochrome c oxidase (Complex IV) do?

Answer 22

catalyze the transfer of electrons from the reduced form of cytochrome c to molecular oxygen

Question 23

How many electrons are funneled to O2 to completely reduce it to H2O?

Answer 23

4

Question 24

T/F

The copper centers of Complex IV alternate between Cu+ and Cu2+ as they accept and donate electrons.

Answer 24

True

Question 25

Where is the active center of Complex IV where O2 is completely reduced to H2O?

Answer 25

Heme a3 and CuB, which are directly adjacent

Question 26

What is sequence of electron flow from cytochrome c and Complex IV?

Answer 26

CuA/CuA - a - a3 - CuB

Question 27

Describe the reduction of O2 to H2O

Answer 27

electrons from cytochrome c flow down the pathway, one stopping at CuB and the other at a3
as O2 binds, it takes an electron from each of the nearby ions to form a O2(-2) bridge
two more molecules of cyto c bind and release e-; the two ion-oxygen groups are reduced to CuB-OH, Fe-OH
the addition of two more H+ ions allows the release of of two molecules of H2O and resets the enzyme

Question 28

Where do the 4 protons come from in the reduction of O2 to H2O?

Answer 28

the matrix

Question 29

What are ROS?

Answer 29

reactive oxygen species such as OH radical, which can lead to oxidative cell damage

Question 30

How does the body combat ROS?

Answer 30

through scavenging enzymes, Superoxide dismutase and catalyze which perform their reactions near the diffusion limit

Question 31

What is the chemiosmotic hypothesis?

Answer 31

electron transport and ATP synthesis are coupled by a proton gradient across the inner mitochondrial membrane

Question 32

What is a proton-motive force?

Answer 32

energy rich unequal distribution of protons, which can be thought of as a chemical gradient and a charge gradient

Question 33

Where is F0 subunit?

Answer 33

embedded in the inner mitochondrial membrane

Question 34

What does the F1 subunit contain?

Answer 34

the catalytic activity of the synthase

Question 35

What is important about the gamma subunit?

Answer 35

breaks down the symmetry of the alpha-beta hexamer; each of the beta subunits is distinct by virtue of its interaction with a different face of gamma

Question 36

What are the names of the hydrophilic half channels of the a subunit in F0?

Answer 36

the cytoplasmic half channel

the matrix half channel

Question 37

How do protons “move across” the membrane?

Answer 37

Protons bond to aspartate sidechains in the half channels
the aspartic acid residues then rotate until the proton is in a proton poor environment
the proton is then released

Question 38

What is significant about proton movement in Complex V?

Answer 38

the movement of protons through the half-channels from the high proton concentration of the cytoplasm to the low proton concentration of the matrix powers the rotation of the c ring, this in turn drives the rotation of the gamma subunit (the formation of ATP)

Question 39

How are electrons from cytoplasmic NADH transferred in the liver?

Answer 39

malate-aspartate shuttle

Question 40

Describe the malate-aspartate shuttle (up to the exchange for glutamate).

Answer 40

electrons are transferred from NADH to oxaloacetate forming malate which traverses the IMM in exchange for alpha-ketoG
malate is then oxidized by NAD+ in the matrix to form NADH in a reaction catalyzed by an enzyme in the CAC
the new oxaloacetate molecule undergoes a transamination reaction to form Asp, which can be transported to the cytoplasmic side in exchange for glutamate

Question 41

Describe the malate-aspartate shuttle (from the exchange of glutamate).

Answer 41

glutamate donates an amino group to oxaloacetate, forming aspartate and alph-ketoG
in the cytoplasm, aspartate is deaminated to form oxaloacetate and the cycle is restarted